Thin-film transistor having lightly-doped drain structure

ABSTRACT

There is provided a semiconductor device including a semiconductor circuit formed by semiconductor elements having an LDD structure which has high reproducibility, improves the stability of TFTs and provides high productivity and a method for manufacturing the same. 
     In order to achieve the object, the design of a second mask is appropriately determined in accordance with requirements associated with the circuit configuration to make it possible to form a desired LDD region on both sides or one side of the channel formation region of a TFT.

This application is a division of application Ser. No. 09/387,053 filedAug. 31, 1999 now U.S. Pat. No. 6,359,320.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a structure of a semiconductor devicehaving a semiconductor circuit comprised of semiconductor elements suchas insulated gate transistors and a method for manufacturing the same.More particularly, the invention relates to a structure of asemiconductor device having a semiconductor circuit comprised ofsemiconductor elements having an LDD structure formed of organic resinand a method for manufacturing the same. Semiconductor devices accordingto the invention include not only elements such as thin film transistors(TFTs) and MOS transistors but also displays having a semiconductorcircuit and electro-optical devices such as image sensors formed by suchinsulated gate transistors. In addition, semiconductor devices accordingto the invention include electronic equipments loaded with such displaysand electro-optical devices.

2. Description of the Related Art

TFTs have been conventionally used as switching elements of activematrix liquid crystal displays (hereinafter abbreviated to read “AMLCD”) The market is currently dominated by products having circuits formedby TFTs utilizing an amorphous silicon film as an active layer.Particularly, a widely used TFT structure is the reverse staggeredstructure, which allows simple manufacturing steps.

However, the accelerating trend toward AMLCDs with higher performance inrecent years has resulted in more severe requirements on the operationalperformance (especially, operating speed) of TFTs. It has thereforebecome difficult to provide elements having sufficient performanceutilizing TFTs comprising amorphous silicon films because of theiroperating speed.

Under such circumstances, TFTs utilizing polycrystalline silicon films(polysilicon films) have come into focus in place of amorphous siliconfilms, which has significantly accelerated the development of TFTsutilizing a polycrystalline silicon film as an active layer. Presently,some products have already been introduced.

Many reports have already been made on structures of reverse staggeredTFTs utilizing a polycrystalline silicon film as an active layer.However, conventional reverse staggered structures have had variousproblems.

First, since an active layer as a whole employed in such structures isas very thin as about 50 nm, impact ionization occurs at the junctionbetween a channel formation region and a drain region, which results insignificant deteriorating phenomena such as the implantation of hotcarriers. This necessitates the formation of an LDD region (light dopeddrain region).

It is expected that at least eight masks are required (for processes upto the formation of source and drain electrodes) to form such an LDDregion in a conventional reverse staggered TFT structure.

As described above, in a conventional reverse staggered TFT structure,an LDD region must be formed in a horizontal plane on both sides or oneside of a channel formation region, which makes it very difficult toform LDD regions with reproducibility.

It is an object of the invention to provide a technique formanufacturing semiconductor devices with high mass-productivity,reliability and reproducibility through very simple manufacturing steps.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided asemiconductor device including a semiconductor circuit formed bysemiconductor elements, characterized in that it comprises:

a gate line provided on an insulated surface;

a gate insulating film in contact with the gate line;

a channel formation region provided on the gate line with the gateinsulating film interposed therebetween;

a low density impurity region in contact with the channel formationregion;

a high density impurity region in contact with the low density impurityregion;

a protective film in contact with the channel formation region; and

organic resin doped with a trivalent or pentavalent impurity in contactwith the protective film.

According to a second aspect of the invention, there is provided asemiconductor device including a semiconductor circuit formed bysemiconductor elements, characterized in that it comprises:

a gate line provided on an insulated surface;

a gate insulating film in contact with the gate line;

a channel formation region provided on the gate line with the gateinsulating film interposed therebetween;

a low density impurity region provided on one side of the channelformation region;

a drain region constituted by a first high density impurity region incontact with the low density impurity region;

a source region constituted by a second high density impurity regionprovided on the other side of the channel formation region;

a protective film in contact with the channel formation region; and

organic resin doped with a trivalent or pentavalent impurity in contactwith the protective film.

According to a third aspect of the invention, there is provided asemiconductor device including a semiconductor circuit formed bysemiconductor elements, characterized in that it comprises:

a gate line provided on an insulated surface;

a gate insulating film in contact with the gate line;

a channel formation region provided on the gate line with the gateinsulating film interposed therebetween;

a first low density impurity region and a second low density impurityregion in contact with the channel formation region;

a high density impurity region on contact with the first low densityimpurity region and the second low density impurity region;

a protective film in contact with the channel formation region; and

organic resin doped with a trivalent or pentavalent impurity in contactwith the protective film and in that the width of the first low densityimpurity region in the direction of the channel length is different fromthe width of the second low density impurity region in the direction ofthe channel length.

There is provided a configuration according to each of theabove-described aspects, characterized in that the gate line has asingle-layer or multi-layer structure and is made of one kind of elementselected from among tantalum, copper, chromium, aluminum, molybdenum,titanium and silicon or a material primarily constituted by silicondoped with a p-type or n-type impurity.

There is provided a configuration according to each of theabove-described aspects, characterized in that the trivalent orpentavalent impurity is phosphorus or boron.

There is provided a configuration according to each of theabove-described aspects, characterized in that the organic resin hasphotosensitivity.

There is provided a configuration according to each of theabove-described aspects, characterized in that the density of thetrivalent or pentavalent impurity in the organic resin is 1×10¹⁹atoms/cm³ or more.

There is provided a configuration according to each of theabove-described aspects, characterized in that a catalytic element forpromoting the crystallization of silicon is included in the high densityimpurity region.

It is also characteristic of the invention that the catalytic element isat least one or a plurality of elements selected from among Ni, Fe, Co,Pt, Cu and Au and that the catalytic element is Ge or Pb.

In the context of the present specification, “initial semiconductorfilm” is a generic term for semiconductor films which typically meanssemiconductor films having amorphous properties, e.g., amorphoussemiconductor films (amorphous silicon films and the like), amorphoussemiconductor films including micro-crystals and micro-crystalsemiconductor films. Such semiconductor films include Si films, Ge filmsand compound semiconductor films (e.g., Si_(x)Ge_(1−x) (0<X<1) which isan amorphous silicon germanium film, “x” typically being in the rangefrom 0.3 to 0.95. Such an initial semiconductor film can be formedusing, for example, low pressure CVD, thermal CVD, PCVD, sputtering orthe like.

In the context of the present specification, the term “crystallinesemiconductor film” implies single crystal semiconductor films andsemiconductor films including grain boundaries (includingpolycrystalline semiconductor films and micro-crystal semiconductorfilms) and clearly distinguishes them from semiconductors which are inan amorphous state in its entirety (amorphous semiconductor films). Whenthe term “semiconductor film” is used in the present specification, itobviously implies not only crystalline semiconductor films but alsoamorphous semiconductor films.

In the context of the present specification, the term “semiconductorelement” implies switching elements and memory elements, e.g., thin filmtransistors (TFTs) and thin film diodes (TFDs).

A first method for manufacturing a semiconductor device including asemiconductor circuit formed by semiconductor elements according to theinvention is characterized in that it comprises:

a first step of sequentially forming a gate insulating film and aninitial semiconductor film on an insulated surface having gate linesformed thereon such that they are stacked without being exposed to theatmosphere;

a second step of crystallizing the initial semiconductor film byirradiating it with infrared light or. ultraviolet light to form acrystalline semiconductor film and an oxide film simultaneously; and

a third step of covering a region to become a channel formation regionof the crystalline semiconductor film with a mask and doping a region tobecome a source region or drain region of the crystalline semiconductorfilm with the trivalent or pentavalent impurity element through theoxide film.

The first method of manufacture described above is further characterizedin that it comprises a step of retaining a catalytic element forpromoting the crystallization of silicon in contact with the surface ofthe initial semiconductor film or within the film after the first step.

According to the present invention, there is provided a second methodfor manufacturing a semiconductor device including a semiconductorcircuit formed by semiconductor element, characterized in that itcomprises the steps of:

sequentially forming a gate insulating film, an initial semiconductorfilm and an insulating film on an insulated surface having gate linesformed thereon such that they are stacked without being exposed to theatmosphere;

crystallizing the initial semiconductor film by irradiating it withinfrared light or ultraviolet light through the insulating film to forma crystalline semiconductor film; and

covering a region to become a channel formation region of thecrystalline semiconductor film with a mask and doping a region to becomea source region or drain region of the crystalline semiconductor filmwith a trivalent or pentavalent impurity element through the insulatingfilm.

The second method of manufacture described above is furthercharacterized in that the gate insulating film, initial semiconductorfilm and protective film are formed using different chambers.

The second method of manufacture described above is furthercharacterized in that the gate insulating film, initial semiconductorfilm and protective film are formed using the same chamber.

The second method of manufacture described above is furthercharacterized in that the gate insulating film and protective film areformed using a first chamber and the initial semiconductor film isformed using a second chamber.

The configuration of each of the methods for manufacture described aboveis characterized in that contaminants on the surface on which theinitial semiconductor film is to be formed are reduced using activehydrogen or a hydride.

The configuration of each of the methods for manufacture described aboveis characterized in that it comprises the step of forming a multi-layerfilm including a silicon nitride film as any of the layers as the gateinsulating film.

The configuration of each of the methods for manufacture described aboveis characterized in that it comprises the step of forming a multi-layerfilm including BCB (benzocyclobutene) as a part of the gate insulatingfilm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing an example of a structure of asemiconductor device according to a first embodiment of the invention.

FIGS. 2A and 2B are plan views of a pixel matrix circuit and a CMOScircuit of the first embodiment.

FIGS. 3A through 3F illustrate steps for manufacturing TFTs according tothe first embodiment.

FIGS. 4A through 4E illustrate steps for manufacturing TFTs according tothe first embodiment.

FIG. 5 is a sectional view showing another example of a structure of asemiconductor device according to a fifth embodiment of the invention.

FIG. 6 is a sectional view showing another example of a structure of asemiconductor device according to a sixth embodiment of the invention.

FIGS. 7A and 7B are sectional views of an example of a pixel matrixcircuit portion according to a seventh embodiment of the invention, andFIG. 7C is a plan view of the same.

FIGS. 8A, 8B and 8C are a circuit diagram of an inverter, a plan view ofthe same and sectional views of examples of sectional structures of thesame according to an eighth embodiment of the invention.

FIG. 9 show a circuit diagram and a sectional structure of a buffercircuit according to a ninth embodiment of the invention.

FIG. 10 illustrates a configuration of a semiconductor device (liquidcrystal display) according to a tenth embodiment of the invention.

FIGS. 11A through 11F show examples of semiconductor devices (electronicequipments) according to a twelfth embodiment of the invention.

FIGS. 12A through 12D show examples of semiconductor devices (electronicequipments) according to the twelfth embodiment of the invention.

FIG. 13 illustrates an example of a film forming device according to thefirst embodiment.

DETAILED DESCRIPTION OF PRFEREED EMBODIMENTS

Modes for carrying out the invention having the above-describedconfigurations will now be described with reference to embodimentdisclosed below.

A first embodiment will now be described. A typical embodiment of thepresent invention will now be described with reference to FIGS. 1through 4. The present embodiment will be described with reference to aCMOS circuit that forms a part of a peripheral driving circuit portionand a pixel TFT that forms a part of a pixel matrix circuit portionprovided on the same substrate. A description will be made withreference to FIGS. 3 and 4 on a method for manufacturing a semiconductordevice including a semiconductor circuit formed by semiconductorelements according to the invention.

A substrate 100 is first prepared. The substrate 100 may be a glasssubstrate, a quartz substrate, an insulating substrate such ascrystalline glass, a ceramic substrate, a stainless steel substrate, ametal (tantalum, tungsten, molybdenum or the like) substrate, asemiconductor substrate, a plastic substrate (polyethylene terephtalatesubstrate) or the like. In the present embodiment, a glass substrate(Coning 1737 having a distortion point at 667° C.) is used as thesubstrate 100.

Next, an underlying film 101 is formed on the substrate 100. A siliconoxide film, a silicon nitride film, a silicon nitride oxide film(SiO_(x)N_(y)) or a multi-layer consisting of such films may be used asthe underlying film 101. The underlying film 101 may have a thickness inthe range from 200 to 500 nm. In the present embodiment, a siliconnitride film having a thickness of 300 nm was formed as the underlyingfilm 101 to prevent contaminant from spreading from the glass substrate.Although the present invention may be implemented without the underlyingfilm, the underlying film is preferably provided to achieve good TFTcharacteristics.

A gate line 102 having a single-layer or multi-layer structure is formed(FIG. 3A). The gate line 102 has a structure including at least onelayer primarily constituted by silicon (Si), silicide or the like dopedwith a conductive material or a semiconductor material, e.g., aluminum(Al), tantalum (Ta), copper (Cu), niobium (Nb), hafnium (Hf), zirconium(Zr), titanium (Ti), chromium (Cr) or a p-type or n-type impurity. Inthe present embodiment, the gate line 102 has a multi-layer structureconstituted by a tantalum layer 102 a having a tantalum oxide layer 102b on the surface thereof. In the present embodiment, the gate line wasformed by patterning a tantalum film and by oxidizing the surfacethereof through anodization thereafter. Tantalum is a preferablematerial that causes less shift of the threshold of a TFT because itswork function is close to that of silicon. The gate line 102 usedpreferably has a thickness in the range from 10 to 1000 nm, morepreferably, in the range from 30 to 300 nm. A step may be adopted toform an anodic film or insulating film only on the surface or uppersurface of the gate line. In order to prevent impurities from spreadingfrom the substrate and gate line to the gate insulating film duringmanufacture, a step may be added to form an insulating film to cover thegate line and substrate. When a multiplicity of gate lines are formedfrom a large substrate, at least one layer made of copper may be formedon the gate lines using plating or sputtering. Which is preferable inreducing the resistance of the line.

Next, a gate insulating film 103 and a semiconductor film 104 aresequentially formed into a multiplicity of layers without exposing themto the atmosphere (FIG. 3B). While any means such as plasma CVD andsputtering may be used to form them at this time, it is important toblock them from the atmosphere in order to prevent any contaminant inthe atmosphere from sticking to any layer interface. Active hydrogen ora hydride is preferably used on the surface on which the semiconductorfilm is to be formed immediately before the formation of the film inorder to reduce contaminant.

In the present embodiment, a silicon nitride oxide film having athickness of 125 nm and an amorphous silicon film having a thickness of50 nm were formed as the gate insulating film 103 and semiconductor film104 respectively to into a multi-layer structure. Obviously, thethickness of each of the films is not limited to the present embodimentand may be appropriately determined by a person who carries out theinvention. In the present embodiment, the multi-layer structure wasformed by using a multi-chamber (an apparatus as shown in FIG. 13)including a first chamber 44 exclusively used to form the gateinsulating film and a second chamber 45 exclusively used to form thesemiconductor film (an amorphous silicon film in this case) and bymoving the films through the chambers without exposing them to theatmosphere. The multi-layer structure may also be formed using the samechamber with the reactive gas replaced.

A silicon oxide film, a silicon nitride film, a silicon nitride oxidefilm (SiO_(x)N_(y)), a multi-layer film consisting of them or the likehaving a thickness in the range from 100 to 400 nm (typically in therange from 150 to 250 nm) may be used as the gate insulating film 103.While the present embodiment employs a single-layer insulating film asthe gate insulating film, a multi-layer structure consisting of two,three or more layers may be used.

The semiconductor film 104 may be an amorphous silicon film, anamorphous semiconductor film including microcrystals, a microcrystallinesemiconductor film, an amorphous germanium film, an amorphous silicongermanium film expressed by Si_(x)Ge_(1−x) (0<X<1) or a multi-layer filmconsisting of them having a thickness in the range from 20 to 70 nm(typically in the range from 40 to 50 nm).

When the state shown in FIG. 3B is thus achieved, the semiconductor film104 is irradiated with infrared light or ultraviolet light to becrystallized (hereinafter referred to as “laser crystallization”). Inthe present embodiment, the irradiation with infrared light orultraviolet light is carried out in the atmosphere, in oxygen or in anoxidizing atmosphere to form the oxide film 105 simultaneously with theformation of the crystalline semiconductor film 106 through lasercrystallization. When ultraviolet light is used for the crystallizationtechnique, excimer laser light or intense light generated by anultraviolet lamp may be used. When infrared light is used, infraredlaser light or intense light generated by an infrared lamp may be used.Excimer laser light is shaped into linear beams to be used forirradiation according to the present embodiment. Referring toirradiating conditions, the pulse frequency is 150 Hz; the overlap ratiois in the range from 80 to 98% (actually, 96% in the presentembodiment); and the laser energy density is in the range from 100 to500 mJ/cm² and, preferably, in the range from 280 to 380 mJ/cm²(actually, 350 mJ/cm² in the present embodiment). Referring toconditions for laser crystallization (laser light wavelength, overlapratio, irradiation intensity, pulse width, repetitive frequency,irradiation time and the like) may be appropriately determined by theperson who carries out the invention in consideration to the thicknessof the semiconductor film 104, the substrate temperature and the like.Depending on the conditions for laser crystallization, the semiconductorfilm may be crystallized after being melted, and the semiconductor filmmay be crystallized in a solid phase or in a state which is intermediatebetween solid and liquid phases without being melted. Laser light iscontinuously moved at a constant speed to keep the overlap ratioconstant in any region with variation of ±10%.

While laser crystallization is used as the crystallizing technique inthe present embodiment, other well-known means such as solid stateepitaxy with and without a catalytic element. While an oxide film isformed simultaneously with laser crystallization according to thepresent embodiment, a step may be employed to form a thin insulatingfilm (a silicon oxide film, silicon nitride film, silicon nitride oxidefilm or the like) before or after the laser irradiation or to performlaser crystallization in an inert atmosphere so as not to form an oxidefilm.

The step shown in FIG. 3C may be followed by a step of selectivelydoping the channel formation region with an impurity in order to controlthe threshold.

Next, the gate insulating film, crystalline semiconductor film and theoxide film are patterned to form an active layer 107 and a firstprotective film 108 (FIG. 3D). The patterning may be carried out after asubsequent step of doping with an impurity.

Next, a second protective film 109 constituted by a nitride film isformed on the entire surface of the substrate to protect the activelayer (FIG. 3E). The second protective film 109 may be a silicon oxidefilm, silicon nitride film, silicon nitride oxide film (SiO_(x)N_(y)) ora multi-layer film consisting of them having a thickness in the rangefrom 3 to 200 nm (typically in the range from 25 to 50 nm). Aconfiguration excluding such a second protective film may be employed.

A first mask (a resist mask in the present embodiment) 110 a having athickness in the range from 1 to 3 μm is then formed in contact with thesecond protective film 109 over the gate line by means of exposure tolight from the rear surface (FIG. 3F). Referring to the material for thefirst mask, a positive or negative type photosensitive organic material(e.g., photoresist, photosensitive polyamide or the like), organic resin(polyimide, polyimide amide, polyamide or the like), a silicon oxidefilm, a silicon nitride film or silicon nitride oxide film(SiO_(x)N_(y)) may be used.

The first mask may be formed by patterning an inorganic insulating filmand leaving the patterning mask made of organic resin therefor as it is,and this provides a multi-layer structure in which the inorganicinsulating film is the lower layer and the organic resin is the upperlayer.

Since no mask is required for the formation of resist through exposureto light from the rear surface, the number of masks required formanufacture can be reduced. While the present embodiment has referred toan example wherein the width of the first mask in the direction of thechannel length is slightly smaller than the width of the gate linebecause of wraparound of light, they may be substantially the same, anda person who carries out the invention may change the width of the firstmask in the direction of the channel length appropriately.

The present specification is based on an assumption that the directionof departing from the substrate 100 is an upward direction and thedirection of approaching the substrate is a downward direction when thesubstrate 100 is cut in a plane perpendicular to the surface thereof.

A first impurity is added through the first protective film 108 andsecond protective film 109 using the first mask 110 a to form a lowdensity impurity region (n⁻-type region) 111 (FIG. 4A). The presentembodiment employs phosphorus as the impurity to provide n-typeconductivity which is adjusted such that the n⁻type region indicated by111 has a phosphorus density in the range from 1×10¹⁵ to 1×10¹⁷atoms/cm³ on the basis of SIMS analysis. At this time, the first mask isdoped with phosphorus to become a first mask 110 b containing a lowdensity of phosphorus.

Next, a second mask (made of photosensitive polyimide resin in thepresent embodiment) 113 a having a thickness in the range from 1 to 3 μmis formed in contact with the second protective film 109 or first mask110 b of the n-channel type TFT (FIG. 4B). Referring to the material forthe second mask, a positive or negative type photosensitive organicmaterial (e.g., resist, photosensitive polyimide or the like), organicresin (polyimide, polyimide amide, polyamide or the like), a siliconoxide film, a silicon nitride film or silicon nitride oxide film(SiO_(x)N_(y)) may be used.

A second impurity is added to form a high density impurity region(n⁺-region) 114 through the first protective film 108 and secondprotective film 109 using the second mask 113 a (FIG. 4C). In thepresent embodiment, the second mask is patterned into a desiredconfiguration to allow an LDD region to be formed with highcontrollability. In the present embodiment, an adjustment is made suchthat the n⁺-type region indicated by 114 has a phosphorus density in therange from 1×10²⁰ to 8×10²² atoms/cm³ on the basis of SIMS analysis. Afirst mask 110 c of the p-channel type TFT is doped with a high densityof phosphorus. A second mask 113 b is similarly doped with a highdensity of phosphorus. A first mask 110 b and a second mask 113 b at thechannel formation region of the n-channel type TFT prevent the channelformation region from being doped with phosphorus.

The first and second steps of doping with impurities form an LDDstructure. The boundary between the n⁻-type and n⁺-type regions isdetermined by the pattern of the second mask. The n⁺-type region 114 ofthe n-channel type TFT serves as a source or drain region, and then⁻-type region serves as a low density impurity region (LDD region) 115.

At the first and second steps of doping with impurities, the first masks110 b and 110 c and the second mask 113 b doped with phosphorus aredarkened. A step may be added to darken the first masks and the secondmask further.

Next, the n-channel type TFT is covered with a third mask 116 and isdoped with a third impurity through the first and second protectivefilms 108 and 109, thereby forming a high density impurity region(p-type region) 117 (FIG. 4D). In the present embodiment, boron is usedas an impurity to provide p-type conductivity, and the dose of boron isset such that the density of boron ions in the p-type region is greaterthan the density of the phosphorus ions added to the n⁺-type region by afactor in the range from about 1.3 to 2. A first mask 110 d of thep-channel type TFT is doped with boron at a high density. Similarly, athird mask 116 is doped with boron. The first, second and third masks,i.e., organic resin, include a trivalent impurity (boron in thisembodiment) or a pentavalent impurity (phosphorus in this embodiment) ata density of 1×10¹⁹ atoms/cm³ or more. The p-type region 117 of thep-channel type TFT serves as a source or drain region. The region whichhas been doped with neither phosphorus ions nor boron ions becomes anintrinsic or substantially intrinsic channel forming region 112 to serveas a carrier moving path later.

In the context of the present specification, an intrinsic region is aregion which does not include any impurity that can cause the Fermilevel of silicon, and a substantially intrinsic region is a region inwhich electrons and holes are perfectly balanced to cause conductivitytypes to cancel each other, i.e., a region including an impurity toprovide the n-type or p-type conductivity at a density range in whichthreshold control is possible (in the range from 1×10¹⁵ to 1×10¹⁷atoms/cm³ on the basis of SIMS analysis) or a region which isintentionally doped with opposite conductivity type impurity to causethe conductivity types to cancel each other.

The doping with the first through third impurities may be carried outusing well-known means such as ion implantation, plasma doping and laserdoping. The doping conditions, dose, acceleration voltage and the likeare adjusted such that a desired amount of impurity ions penetratethrough the first protective film 108 and the second protective film 109to be added to a predetermined region of the active layer.

Further, no contaminant especially boron enters the active layer fromthe atmosphere because impurities are implanted from above the secondprotective film 109 at the first, second and third steps of doping withimpurities. Since it is therefore possible to control the density of theimpurities in the active layer, fluctuation of the threshold can besuppressed.

After the high density impurity region 117 to serve as a source or drainregion is thus formed, only the third mask 116 is selectively removed.The selective removing step may be implemented by using a materialdifferent from that for the first and second masks for the third mask.The first and second protective films 108 and 109 serve as an etchingstopper at this mask removing step. No contaminant enters thecrystalline semiconductor film especially the channel formation region112 at this mask removing step because the first and second protectivefilms have been formed.

A well-known technique, e.g., thermal annealing or laser annealing isthen performed to achieve the effect of activating the impurity in thesource and drain regions or the effect of recovering the crystalstructure of the active layer which has been damaged at the doping step.

Finally, a layer insulating film 118 is formed which is made of organicresin such as polyimide, polyimideamide, polyamide or acrylic orconstituted by a silicon oxide film, a silicon nitride film, a siliconnitride oxide film (expressed by SiO_(x)N_(y)) or a multi-layer filmconsisting of them; contact holes are formed to expose the source anddrain regions; and, thereafter, a metal film is formed and patterned toform metal lines 119 through 123 in contact with the source and drainregions (FIG. 4E). This completes the manufacture of a CMOS circuitportion formed by n-channel type and p-channel TFTs and a pixel matrixcircuit portion formed by n-channel type TFTs according to a mode forcarrying out the invention.

A description will now be made with reference to FIG. 1 on aconfiguration of a semiconductor device including a semiconductorcircuit utilizing semiconductor elements formed according to theabove-described manufacture steps. In the present embodiment, forsimplicity, the illustration shows only a CMOS circuit portion forming apart of a peripheral driving circuit portion and pixel TFTs (n-channeltype TFTs) forming a part of a pixel matrix circuit portion on the samesubstrate.

FIGS. 2A and 2B are plan views associated with FIG. 1. In FIGS. 2A and2B, the section cut along the dotted line A-A′ corresponds to thesectional structure of the pixel matrix circuit portion in FIG. 1, andthe section cut along the dotted line B-B′ corresponds to the sectionalstructure of the CMOS circuit portion in FIG. 1. The reference numbersused in FIGS. 1, 2A and 2B are the same as those used in FIGS. 3Athrough 3F and FIGS. 4A through 4E. For simplicity of illustration,FIGS. 2A and 2B do not show the first and second masks.

In FIG. 1, all of the TFTs (thin film transistors) are formed on theunderlying film 101 provided on the substrate 100. For the p-channeltype TFT in the CMOS circuit, the gate line 102 is formed on theunderlying film, and the gate insulating film 103 is provided on thesame. The p-type region 117 (source or drain region) and the channelformation region 112 are formed as active layers on the gate insulatingfilm. The active layers are protected by the first protective film 108and the second protective film 109 which have the same pattern. Contactholes are formed on the first layer insulating film 118 made of organicresin covering the second protective film 109 to connect the lines 119and 120 to the p-type region 117. A second layer insulating film 125 isformed thereon; an extraction line 126 is connected to the line 119 anda third layer insulating film 129 is formed thereon to cover the same.The first mask 110d having light blocking properties is formed on thesecond protective film over the channel formation region to protect thechannel formation region from deterioration. The first mask 110 d isdoped with a trivalent impurity (boron in the present embodiment) and apentavalent impurity (phosphorus in this embodiment) at a density of1×10¹⁹ atoms/cm³ or more.

The n-channel type TFT is formed with the n⁺-type regions 114 (source ordrain region) as active layers, the channel formation region 112 and then⁻-type region (LDD region) 115 between the n⁺-type region (drainregion) and the channel formation region. The lines 120 and 121 arerespectively formed in the drain region and source region among then⁺-type regions 114, and the lead line 127 is further connected to theline 121. Its structure is substantially the same as that of thep-channel type TFT in regions other than the active layer. The firstmasks (100 b and 110 c) are formed at least on the second protectivefilm over the channel formation region 112, and a second mask 113 bhaving light blocking properties is formed on the second protective filmover the drain region which is one of the n⁻-type regions 114 to protectthe channel formation region and the n⁻-type regions from thedeterioration of light.

The n-channel type TFTs formed in the pixel matrix circuit have the samestructure as that of the n-channel TFT of the CMOS circuit up to theregion where the gate insulating film 103 is formed. In the n-channeltype TFTs formed in the pixel matrix circuit, since deterioratingphenomena such as hot carrier implantation can occur between the n⁺-typeregions 114 and the channel formation regions 112 connected to the lines122 and 123, the n⁻-type regions (LDD regions) 115 are formed betweenthe n⁺-type regions and channel formation regions connected to thelines, and no n⁻-type region (LDD region) is provided between adjoiningchannel formation regions. The first and second masks used to form then⁻-type regions (LDD regions) 115 are left as they are to be used aslight-blocking films. The second layer insulating film 125 and a blackmask 128 are formed on the first layer insulating film 118 with thelines 122 and 123 formed thereon. The third layer insulating film 129 isformed thereon, and a pixel electrode 130 constituted by a transparentconductive film made of ITO, SnO₂ or the like is connected to the same.The black mask covers the pixel TFTs and cooperates with the pixelelectrode 130 to form an auxiliary capacity.

In the present embodiment, since a resist mask is formed throughexposure to light at the rear surface, a mask is provided over the gateline to reduce any capacity that the gate line forms with the lines.

While a transmission type LCD is manufactured as an example in thepresent embodiment, the invention is not limited thereto. For example, areflective metal material may be used as the material for the pixelelectrode, and a reflection type LCD may be manufactured by changing thepatterning of the pixel electrode or adding and deleting several stepsappropriately.

While the gate lines of the pixel TFTs of the pixel matrix circuit havea double gate structure in the present embodiment, a multi-gatestructure such as a triple gate structure may be used to reducevariation of the off-current. A single gate structure may be used toimprove the numerical aperture.

A second embodiment will now be described. The present embodiment is anexample in which a crystalline semiconductor film is obtained using amethod different from that in the first embodiment. In the presentembodiment, a step is added between the steps shown in FIGS. 3B and 3Cof the first embodiment to cause a catalytic element for promotingcrystallization to be carried on the entire surface of the semiconductorfilm or to be selectively carried. Since the present embodiment issubstantially the same as the first embodiment in the basicconfiguration, the following description will address only differencesbetween them.

The present embodiment is identical to the first embodiment up to thestep of forming the semiconductor film 104 (FIG. 3B).

According to the present embodiment, a catalytic element for promotingthe crystallization of silicon is introduced on the surface of thesemiconductor film 104. As the catalytic element for promoting thecrystallization of silicon, one or a plurality of elements selected fromamong Ni, Fe, Co, Pt, Cu, Au and Ge are used. In the present embodiment,Ni is used among the catalytic elements because of its high speed inspreading in an amorphous silicon film and its excellent crystallinity.

The introduction of the catalytic element is not limited to anyparticular locations, and the element is introduced on the entiresurface of the amorphous silicon film or selectively on the surface byforming a mask appropriately. A step may be employed to introduce thecatalytic element on the rear surface of the amorphous silicon film oron both of the front and rear surfaces.

There is no limitation on the method for introducing a catalytic elementto the amorphous silicon film as long as it allows the catalytic elementto be put in contact with the surface of the amorphous silicon film orit allows the catalytic element to be retained in the amorphous siliconfilm. For example, it is possible to adopt sputtering, CVD, plasmaprocessing, absorption, ion implantation or a method of applying asolution including a catalytic element. The method utilizing a solutionis easy to implement and is advantageous in that the density of acatalytic element can be easily adjusted. Various salts may be used asthe metallic salt, and usable solvents other than water includealcohols, aldehydes, ethers, other organic solvents or solvents obtainedby mixing water and organic solvents. In the present embodiment, themethod of applying a solution is used to apply a solution includingnickel in the range from 10 to 10000 ppm and, preferably, in the rangefrom 100 to 10000 ppm (by weight). The dose must be adjustedappropriately in consideration to the thickness of the amorphous siliconfilm. The density of nickel in the amorphous silicon film thus obtainedis in the range from 1×10¹⁹ to 1×10²¹ atoms/cm³.

After a catalytic element is introduced into the amorphous silicon filmas described above, crystallization is conducted by irradiating the filmwith laser light to obtain a crystalline silicon film. A heating step ata high temperature may be added in place of the irradiation with laserlight. A gettering step may be added to reduce the number of catalyticelements in the film.

Subsequent steps provide a semiconductor device as shown in FIG. 1according to the first embodiment.

A third embodiment of the invention will now be described. The presentinvention is an example in which a crystalline semiconductor film isobtained using a method different from that for the first embodiment. Inthe present embodiment relates to a method wherein laser beams areshaped into a rectangular or square configuration to perform a uniformlaser crystallization process throughout an area in the range fromseveral cm² to several hundred cm² with irradiation at one time, therebyproviding a crystalline silicon film. Since this embodiment issubstantially the same as the first embodiment in its basicconfiguration, the description will address only differences betweenthem.

According to the present embodiment, irradiation is conducted withexcimer laser light which is processed into a planar configuration atthe step shown in FIG. 3C. The laser light must be processed into aplanar configuration such that an area on the order of several tens cm²(preferably 10 cm²) or more can be irradiated at a time. In order toanneal the irradiated surface as a whole with a desired laser energydensity, a laser apparatus that provides output having total energy of 5J or more and preferably 10 J or more is used.

In this case, the energy density is in the range from 100 to 800 mJ/cm²,and the output pulse width is 100 nsec. or more and is preferably in therange from 200 nsec. to 1 msec. A pulse width in the range from 200nsec. to 1 msec. can be achieved by connecting a plurality of laserdevices and by operating the laser devices asynchronously to achieve astate of mixture of a plurality of pulses.

The use of laser light having a planar beam configuration as in thepresent embodiment makes it possible to irradiate a large area withuniform laser light. That is, the active layer will have uniformcrystallinity (in terms of also grain size and defect density), andvariation of electrical characteristics of TFTs can be reduced.

The present embodiment can be easily combined with the first or secondembodiment in flexible modes of combination.

A fourth embodiment of the invention will now be described. The presentembodiment is an example wherein an insulating film and a crystallinesemiconductor film are obtained using a method different from that ofthe first embodiment.

According to the present embodiment, a silicon nitride oxide film havinga thickness of 125 nm as a gate insulating film, an amorphous siliconfilm having a thickness of 50 nm as an initial semiconductor film and asilicon nitride oxide film having a thickness of 15 nm as an insulatingfilm are formed into a multi-layer configuration without being exposedto the atmosphere. Obviously, the thickness of each film is not limitedto the present embodiment and may be appropriately determined by aperson who carries out the invention. A configuration may also beemployed in which a multiplicity of layers are formed by replacingreactive gasses in the same chamber. Active hydrogen or a hydride ispreferably used on the surface on which the film is to be formed beforethe initial semiconductor film is formed to reduce contaminant.

Thereafter, the initial semiconductor film is irradiated with infraredlight or ultraviolet light to be crystallized (hereinafter referred toas “laser crystallization”). In the present embodiment, excimer laserlight is shaped into linear beams to be used for irradiation. Referringto irradiating conditions, the pulse frequency is 150 Hz; the overlapratio is in the range from 80 to 98% (96% in the present embodiment);and the laser energy density is in the range from 100 to 500 mJ/cm² and,preferably, in the range from 150 to 200 mJ/cm² (175 mJ/cm² in thepresent embodiment). Referring to conditions for laser crystallization(laser light wavelength, overlap ratio, irradiation intensity, pulsewidth, repetitive frequency, irradiation time and the like) may beappropriately determined by the person who carries out the invention inconsideration to the thickness of the insulating film, the thickness ofthe initial semiconductor film, the substrate temperature and the like.

This step crystallizes the initial semiconductor film to be transformedinto a crystalline semiconductor film (a semiconductor film includingcrystals). In the context of the present embodiment, a crystallinesemiconductor film is a polycrystalline silicon film. At this step, nocontaminant enters the initial semiconductor film from the atmospherebecause the laser light is projected through the insulating film. Thatis, the initial semiconductor film can be crystallized with theinterface of the initial semiconductor film kept clean.

Thus, substantially the same state as that shown in FIG. 3C is achieved.Subsequent steps (in FIG. 3D and later drawings) complete asemiconductor device as shown in FIG. 1 according to the firstembodiment. The present embodiment can be easily combined with the firstor third embodiment in flexible modes of combination.

A fifth embodiment of the invention will now be described, The presentembodiment refers to an example of the manufacture of a TFT having astructure different from that in the first embodiment with reference toFIG. 5. Plan views of FIG. 5 will correspond to FIGS. 2A and 2B.

According to the present embodiment, a multi-layer structure is providedin which an upper layer is constituted by a plastic substrate as asubstrate 500, silicon nitride oxide (expressed by SiO_(x)N_(y)) as anunderlying film 501 and a film made of a material mainly composed ofcopper (Cu) as a gate line and in which a lower layer is constituted bya film made of a material mainly composed of tantalum.

Next, a film made of an organic material, e.g., BCB (benzocyclobutene)for flattening irregularities between regions having gate lines andregions having no gate line is formed to a thickness in the range from100 nm to 1 μm (preferably in the range from 500 to 800 nm) as a firstinsulating film 503. This step must provide a film thickness sufficientto flatten any step attributable to gate lines completely. Since a BCBfilm has a significant flattening effect, it can provide a sufficientflatness with a not so large thickness.

After the first insulating film 503 is formed, a second insulating film(silicon nitride oxide film) 504, an initial semiconductor film(microcrystalline silicon film) and an insulating film (silicon nitrideoxide film) to serve as a protective film 509 are sequentially formedinto layers without exposing them to the atmosphere. Themicrocrystalline silicon film is formed at a temperature in the rangefrom 80 to 300° C. and preferably in the range from 140 to 200° C. andwith silane gas diluted by hydrogen (SiH₄: H₂=1:10 to 100) as thereactive gas, a gas pressure in the range from 0.1 to 10 Torr anddischarge power in the range from 10 to 300 mW/cm². Since the hydrogendensity in the microcrystalline silicon film is low, the use of the sameas the initial semiconductor film makes it possible to delete a thermalprocess to reduce the hydrogen density. In the present embodiment,separate chambers exclusively used for the second insulating film,initial semiconductor film and protective film are prepared, and thefilms are continuously formed while the substrate is moved through thechambers without being exposed to the atmosphere. The insulating filmand semiconductor film thus formed continuously are flat because theyare formed on the flat surface.

Then, excimer laser light is projected upon the protective film tomodify the semiconductor film into a semiconductor film includingcrystals (polycrystalline silicon film). Conditions for this lasercrystallization may be the same as those in the fourth embodiment. Atthis time, since the semiconductor film is flat, a polycrystallinesilicon film having a uniform grain size can be obtained. Intense light,e.g., RTA or RTP may be used for irradiation instead of laser light.

Since a BCB film which can be easily flattened is used as the firstinsulating film 503, a semiconductor film having a flat surface can beprovided. This makes it possible to maintain uniform crystallinitythroughout the semiconductor film.

Subsequent steps complete a semiconductor device as shown in, forexample, FIG. 5 according to the first embodiment, although there is aslight difference in the design of the second mask.

Referring to FIG. 5, all TFTs (thin film transistors) are formed on anunderlying layer 501 provided on a substrate 500. For a p-channel typeTFT of a CMOS circuit, gate lines 502 a and 502 b are formed on theunderlying layer, and a first insulating film 503 and a secondinsulating film 504 made of BCB are provided thereon. A p-type region508 (source or drain region) and a channel formation region 505 asactive layers are formed on the second insulating film. The activelayers are protected by a protective film 509 having the sameconfiguration. A contact hole is formed through a first layer insulatingfilm 510 covering the protective film 509 to connect lines 511 and 512to the p-type region 508. A second layer insulating film 516 is furtherformed thereon; an extraction line 517 is connected to the line 511; anda third layer insulating film 520 is formed to cover the same. A firstmask having light blocking properties is formed at least on theprotective film over the channel formation region to protect the channelformation region from deterioration attributable to light.

Referring to the n-channel type TFT, an n⁺-type region 507 (source ordrain region), channel formation region 505 and an n⁻-type region 506between the n⁺-type region and channel formation region are formed asactive layers. The n⁺-type region 507 is formed with lines 512 and 513,and an extraction line 518 is connected to the line 513. Regions otherthan the active layers have substantially the same structure as that ofthe p-channel TFT. A first mask having light blocking properties isformed at least on the protective film over the channel formation region505 and a second mask is formed on the protective film over the n⁻-typeregion 506 to protect the channel formation region and n⁻-type regionfrom deterioration attributable to light.

Referring to n-channel type TFTs formed in the pixel matrix circuit,lines 514 and 515 are connected to n⁺-type regions 507, and a secondlayer insulating film 516 and a black mask 519 are formed thereon. Theblack mask covers the pixel TFTs and forms an auxiliary capacity incooperation with the line 515. Further, a third layer insulating film520 is formed therein, and a pixel electrode 521 constituted by atransparent conductive film such as ITO is connected thereto.

The pixel matrix circuit of the present embodiment has a TFT structurein which a line capacity generated between the gate line 502 and thelines 514 and 515 is reduced by the first and second masks. According tothe embodiment, a capacity between lines is reduced not only in thepixel matrix circuit but also in other regions by the masks are providedover the gate line because the resist masks are formed through exposureto light at the rear surface.

TFTs manufactured according to the present embodiment exhibit electricalcharacteristics with less variation. The present embodiment can becombined with the first, second, third or fourth embodiment.

A sixth embodiment of the present invention will now be described. Inthe present embodiment, a description will be made with reference toFIG. 6 on an example of the manufacture of a TFT having a structuredifferent from that in the first embodiment. The configuration of theCMOS circuit will be described only in areas of difference because it issubstantially the same as that in the first embodiment. Plan views ofFIG. 6 correspond to FIGS. 2A and 2B.

The present embodiment is the same as the first embodiment up to theformation of a glass substrate as a substrate, a silicon nitride oxidefilm (SiO_(x)N_(y)) as an underlying film and a gate line.

According to the present embodiment, a first insulating film 601 is thenselectively formed in the pixel matrix circuit.

Thereafter, a second insulating film (which corresponds to the gateinsulating film in the first embodiment) and an initial semiconductorfilm are sequentially formed into a multiplicity of layers withoutexposing them to the atmosphere just as in the first embodiment. In thepresent embodiment, a silicon nitride oxide film having a thickness inthe range from 10 to 100 nm as a second insulating film 602 and anamorphous silicon film having a thickness of 50 nm as an initialsemiconductor film are formed into a multiplicity of layers using plasmaCVD in the same chamber with a high degree of vacuum maintained therein.Obviously, the thickness of each of the films is not limited to thepresent embodiment and may be appropriately determined by a person whocarries out the invention. According to the present embodiment, the gateinsulating films (first insulating film 601 and second insulating film602) of the pixel matrix circuit are formed to provide a total thicknessin the range from 100 to 300 nm.

Description will be omitted for the CMOS circuit in FIG. 6 because ithas substantially the same configuration as that in the firstembodiment. The n-channel type TFTs formed in the pixel matrix circuithave substantially the same as those in FIG. 1 according to the firstembodiment except that the gate insulating film has a two-layerstructure (first insulating film 601 and second insulating film 602). Byselectively increasing the thickness of the gate insulating films asdescribed above, reliability of circuits which must have a highwithstand voltage (pixel matrix circuit, buffer circuit and the like) isimproved.

The pixel matrix circuit of the present embodiment has a TFT structurein which a line capacity generated between the gate line and other linesis reduced by a first and second masks just as in the first embodiment.According to the embodiment, a capacity between lines is reduced notonly in the pixel matrix circuit but also in other regions by the masksare provided over the gate line because the resist masks are formedthrough exposure to light at the rear surface.

TFTs manufactured according to the present embodiment exhibit electricalcharacteristics with less variation. The present embodiment can becombined with any of the first through fifth embodiments.

A seventh embodiment of the present invention will now be described. Inthe present embodiment, a description will be made with reference toFIGS. 7A, 7B and 7C on an example of the manufacture of a pixel matrixcircuit portion having a structure different from that in the firstembodiment. While the gate lines of the pixel TFTs in the pixel matrixcircuit portion of the first embodiment have a double gate structure,the present embodiment refers to an example wherein a triple gatestructure is employed to reduce variation of the off-current.

FIG. 7C is a plan view showing an example of the triple gate structure.FIG. 7A shows an example of the section taken along the dotted line A-A′in FIG. 7C.

In FIG. 7A, 701 represents an n⁻-type region (LDD region); 702represents gate lines; 703 represents an n⁺-type region; 704 and 705represent lines; 706 represents a black mask; 707 represents a pixelelectrode; 708 and 709 represent layer insulating films; and 710represents a second mask. This configuration is characterized in thatthe LDD region (with a width in the direction of the channel length inthe range from 0.5 to 3 μm, typically in the range from 1 to 2 μm) isprovided only in a region where it is required. According to the priorart, especially the self-alignment method, unnecessary LDD regions havebeen formed between adjoining channel formation regions.

The present embodiment may be formed as an application of the firstembodiment. The sectional structure shown in FIG. 7A especially then⁻-type region (LDD region) and n⁺-type region can be easily formed bymodifying the pattern of the second mask of the first embodiment.

Further, the use of a pattern of the second mask different from that inFIG. 7A makes it possible to obtain a different with of the LDD regionas shown in FIG. 7B without any increase in the number of steps. FIG. 7Bis substantially the same as FIG. 7A except that a first n⁻-type region722 having a greater width in the direction of the channel length of theLDD region and a second n⁻-type region 721 having a smaller width in thedirection of the channel length of the LDD region are selectivelyformed. The width of the first n⁻-type region 722 in the direction ofthe channel length is in the range from 0.5 to 3 μm and typically in therange from 1 to 2 μm, and the width of the second n⁻-type region 721 inthe direction of the channel length is in the range from 0.3 to 2 μm andtypically in the range from 0.3 to 0.7 μm. The width of each of then⁻-type regions in the direction of the channel length can be freelyadjusted by the design of the mask. Therefore, the widths of the n⁻-typeregions in the direction of the channel length may be appropriatelydetermined by a person who carries out the invention depending onrequirements associated with the circuit configuration.

TFTs manufactured according to the present embodiment exhibit electricalcharacteristics with less variation. The present embodiment can becombined with any of the first through sixth embodiments.

An eighth embodiment of the present invention will now be described. Inthe present embodiment, a description will be made with reference toFIGS. 8A, 8B and 8C on an example of the circuit configuration of theCMOS circuit (inverter circuit) shown in the first embodiment. Terminalportions a, b, c and d in the inverter circuit diagram and the plan viewof the inverter circuit in FIG. 8A correspond to each other.

The sectional structure along the line A-A′ of the inverter circuit inFIG. 8A is the same as that shown in FIG. 1. Therefore, the structureshown in FIG. 8A can be provided according to the first embodiment. Thiscircuit is formed by gate lines 801, a source electrode 802 of ap-channel type TFT, a source electrode 803 of an n-channel type TFT anda common drain electrode 804.

FIG. 8B shows a sectional structure of the inverter circuit differentfrom the sectional structure along the line A-A′ in FIG. 8A. To providethe structure shown in FIG. 8B, the pattern of a second mask 810 as inthe first embodiment is modified to form a second mask 820 also in thep-channel type TFT, thereby forming a p⁻-type region 822 doped withboron at a low density and an n⁻-type region 821. A mask for achieving alow boron density is required to provide the structure shown in FIG. 8B.

FIG. 8C shows a sectional structure of the inverter circuit differentfrom the sectional structure along the line A-A′ in FIG. 8A. To providethe structure shown in FIG. 8C, the pattern of the second mask 810 as inthe first embodiment is modified to form a second mask 840, therebyforming n⁻-type regions 841 on both sides of the channel formationregion. The width of each of the n⁻-type regions in the direction of thechannel length can be freely adjusted through designing of the mask.Therefore, the width of the n⁻-type regions in the direction of thechannel length may be appropriately determined by a person who carriesout the invention according to requirements associated with the circuitconfiguration. Gate lines 831 are patterned after forming a tantalumfilm and thereafter forming an anodic film on the surface thereof toreduce the number of masks.

The structures shown in FIGS. 8A and 8B can be simultaneously fabricatedon the same substrate without increasing the number of steps. Thepresent invention makes it possible to form n⁻-type regions or p⁻-typeregions having various widths (in the direction of the channel length)on the same substrate. For example, it is possible to simultaneouslyfabricate a TFT having an n⁻-type regions on both sides of the channelformation region, a TFT having an n⁻type region on one side of thechannel formation region, a TFT having n⁻-type regions with differentwidths in the direction of the channel length on both sides of thechannel formation region, a TFT having no n⁻type region on both sides ofthe channel formation region and the like on the same substrate withoutincreasing the number of steps.

The present embodiment may be combined with any one of the first throughsixth embodiments.

A ninth embodiment of the present invention will now be described. Inthe present embodiment, a description will be made with reference toFIG. 9 on an example of a configuration of a buffer circuit utilizingbottom-gate type TFTs shown in the first through sixth embodiments. TheCMOS circuit is formed as a complementary combination of an n-channeltype TFT and a p-channel type TFT formed on the same substrate. Terminalportions a, b, c and d in the buffer circuit diagram and the sectionalstructure view of the buffer circuit in FIG. 9 correspond to each other.

In the buffer circuit, as illustrated, an n⁻-type region is preferablyformed at least one side (the side of an output line terminal b) of thechannel formation region of the n-channel type TFT. To obtain thestructure shown in FIG. 9, the pattern of the second mask 113 of thefirst embodiment is modified to form a second mask 910, thereby formingan n⁻-type region 901 on one side of the channel formation region.

The present embodiment can be combined with any one of the first throughsixth embodiments.

A tenth embodiment of the present invention will now be described. Inthe present embodiment, an example of a liquid crystal displaymanufactured according to the invention will be described with referenceto FIG. 10. Detailed description will be omitted for the method ofmanufacturing the pixel TFTs (pixel switching elements) and the step forcell assembly because they may be carried out using well-known means.

In FIG. 10, 1000 represents a substrate having an insulated surface (aglass substrate having a silicon oxide film provided thereon); 1001represents a pixel matrix circuit; 1002 represents a scan line drivingcircuit; 1003 represents a signal line driving circuit; 1030 representsa counter substrate; 1010 represents an FPC (flexible printed circuit);and 1020 represents a logic circuit. The logic circuit 1020 may beformed as a circuit such as a D-A converter, gamma correction circuit orsignal division circuit having functions which have been conventionallysubstituted by an IC. Obviously, an IC chip may be provided on thesubstrate to perform signal processing on the IC chip.

While the present embodiment refers to a liquid crystal display as anexample, the present invention may obviously be applied to any activematrix type display such as an EL (electro-luminescence) display or EC(electro-chromics) display.

The present invention may be applied to the manufacture of any liquidcrystal display whether it is of the transmission type or reflectiontype. A person who carries out the invention may choose either of themat his or her own choice. Thus, the invention may be any active matrixtype electro-optical device (semiconductor device).

The configuration of any of the first through ninth embodiments may beused to manufacture a semiconductor device as described in the presentembodiment, and any combination of those embodiments may be used.

An eleventh embodiment of the invention will now be described. Theinvention may be applied to conventional IC techniques in general. Thatis, the invention may be applied to all semiconductor circuits currentlyavailable on the market. For example, it may be applied tomicroprocessors such as RISC processors and ASIC processors integratedon one chip and may be applied to signal processing circuits representedby driver circuits for liquid crystal (D-A converters, gamma correctioncircuits, signal division circuits and the like) and to high frequencycircuits for portable devices (potable telephones, PHS and mobilecomputers).

Semiconductor circuits such as microprocessors are loaded on variouselectronic equipments to function as a key circuit. Typical electronicequipment include personal computers, personal digital assistants andall other electronic equipment for home use. Computers for controllingvehicles (automobiles, trains and the like) are also included. Theinvention may be applied to semiconductor devices for such purposes.

The configuration of any of the first through ninth embodiments may beused to manufacture a semiconductor device as described in the presentembodiment, and any combination of those embodiments may be used.

A twelfth embodiment of the invention will now be described. A CMOScircuit and a pixel matrix circuit formed according to the invention maybe used in various electro-optical devices (active matrix type liquidcrystal displays, active matrix type EL displays and active matrix typeEC displays). That is, the invention may be applied to any electronicequipment incorporating such electro-optical devices as display media.

Such electronic equipments include video cameras, digital cameras, (reartype or front type) projectors, head-mount displays (goggle typedisplays), car navigation systems, personal computers and personaldigital assistants (mobile computers, portable telephones, electronicbooks and the like). FIGS. 11A through 11F and FIGS. 12A through 12Dshow examples of such devices.

FIG. 11A shows a personal computer which is formed by a main body 2001,an image input portion 2002, a display 2003 and a keyboard 2004. Theinvention may be applied to the image input portion 2002, display 2003and other signal control circuits.

FIG. 11B shows a video camera which is formed by a main body 2101, adisplay 2102, an audio input portion 2103, operation switches 2104, abattery 2105 and an image receiving portion 2106. The invention may beapplied to the display 2102, audio input portion 2103 and other signalcontrol circuits.

FIG. 11C shows a mobile computer which is formed by a main body 2201, acamera portion 2202, an image receiving portion 2203, operations witches2204 and a display 2205. The invention may be applied to the display2205 and other signal control circuits.

FIG. 11D shows a goggle type display which is formed by a main body2301, a display 2302 and an arm portion 2303. The invention may beapplied to the display 2302 and other signal control circuits.

FIG. 11E shows a player utilizing a recording medium on which a programis stored (hereinafter referred to as “recording medium) and which isformed by a main body 2401, a display 2402, a speaker portion 2403, arecording medium 2404 and operation switches 2405. This device utilizesa DVD (digital versatile disc) CD or the like as the recording mediumand can be used for enjoying music, movies and internet. The inventionmay be applied to the display 2402 and other signal control circuits.

FIG. 11F shows a digital camera which is formed by a main body 2501,adisplay 2502, an eye-piece 2503, operation switches 2504 and an imagereceiving portion (not shown). The invention may be applied to thedisplay 2502 and other signal control circuits.

FIG. 12A shows a front type projector which is formed by a display 2601and a screen 2602. The invention may be applied to the display and othersignal control circuits.

FIG. 12B shows a rear type projector which is formed by a main body2701, a display 2702, a mirror 2703 and a screen 2704. The invention maybe applied to the display and other signal control circuits.

FIG. 12C shows an example of a structure for the displays 2601 and 2702in FIGS. 12A and 12B, respectively in which displays 2601 and 2702 areformed by a light source optical system 2801, mirrors 2802, 2805, 2806and 2807, dichroic mirrors 2803 and 2804, optical lenses 2808, 2809 and2811, liquid crystal displays 2810 and a projection optical system 2812.The projection optical system 2812 is constituted by an optical systemincluding a projection lens. While an example of a three-plate systemutilizing three liquid crystal displays 2810 is described in thisembodiment, the invention is not limited thereto and, for example, asingle-plate system may be used. A person who carries out the inventionmay provide an appropriate optical system such as an optical lens, afilm having a polarizing function, a film for adjusting a phasedifference or an IR film in the light path indicated by the arrow inFIG. 12C.

FIG. 12D shows an example of a structure of the light source opticalsystem 2801 in FIG. 12C. In the present embodiment, the light sourceoptical system 2801 is formed by light sources 2813 and 2814, acomposite prism 2815, collimator lenses 2816 and 2820, lens arrays 2817and 2818 and a polarizing conversion element 2819. While two lightsources are-used in the light source optical system shown in FIG. 12D,three or four. or even more light sources may be used and,alternatively, only one light source may be used. A person who carriesout the invention may provide an appropriate optical system such as anoptical lens, a film having a polarizing function, a film for adjustinga phase difference or an IR film in the light source optical system.

As described above, the present invention has a wide range ofapplication and can be used for electronic equipments in any field. Theconfiguration of an electronic equipment according to the presentembodiment may be any combination of the first through sixthembodiments, and the embodiments may be used in any combination.Electro-optical devices and semiconductor circuits according to theseventh through eleventh embodiments may also be freely combined.

The present invention makes it possible to provide TFTs having an LDDstructure which has high reproducibility, improves the stability of TFTsand provides high productivity.

The use of the invention allows a user to form a desired LDD region onboth sides or one side of the channel formation region of a TFT bydetermining the design for the second mask appropriately in accordancewith requirements associated with the circuit configuration. Forexample, it is possible to form a first n-channel type TFT having afirst LDD region with a width in the direction of the channel length inthe range from 0.5 to 3 μm and typically in the range from 1 to 2 μm anda second n-channel type TFT having a second LDD region with a width inthe direction of the channel length in the range from 0.3 to 2 μm andtypically in the range from 0.3 to 0.7 μm.

The masks used to form an LDD structure can be used as they are aslight-blocking films, thereby protecting the active layer especially thechannel formation region from deterioration associated with light toimprove reliability. TFTs can be manufactured in a short period of timeby deleting the mask removing step.

The use of the present invention makes it possible to form an LDD regionwith a number of masks (seven masks at the minimum) as follows which isless than the number of masks required according to the prior art up tothe formation of a source or drain electrode (eight masks at theminimum).

Mask No. 1 for forming gate lines

Mask No. 2 for forming islands

Mask No. 3 for forming a second mask

Mask No. 4 for forming a doping mask to provide p-type conductivity

Mask No. 5 for forming contact holes for source and drain regions

Mask No. 6 for forming a contact-hole for a gate line

Mask No. 7 for forming source and drain electrodes

Since the present invention can be carried out using a conventionalproduction line for amorphous silicon TFTs as it is only by introducingseveral devices, there are industrial advantages.

In addition, since masks serve as insulating films at intersectionsbetween gate lines and other lines, a line capacity can be reduced toimprove the electrical characteristics of a TFT.

By forming a gate insulating film and a semiconductor film into amultiplicity of layers without exposing them to the atmosphere, a quiteclean interface can be provided between them. Especially, since such aconfiguration makes it possible to keep an interface between an activelayer and a gate insulating film which determines the electricalcharacteristics of TFTs clean, TFTs having less variation and preferableelectrical characteristics can be provided.

The threshold voltage which is a typical parameter of a TFT can be inthe range from −0.5 to 2 V for an n-channel type TFT and can be in therange from 0.5 to −2 V for a p-channel type TFT. A sub-thresholdcoefficient (S-value) in the range from 0.1 to 0.3 V/decade can beachieved.

What is claimed is:
 1. A semiconductor device comprising: a pixel matrixcircuit over an insulating surface, having a plurality of pixels, eachof the plurality of pixels comprising at least a thin film transistor,the thin film transistor comprising: a gate line formed on theinsulating surface; a gate insulating film comprising a first insulatingfilm comprising an organic material and a second insulating filmcomprising silicon nitride over the first insulating film, in contactwith the gate line; a channel formation region formed over the gate linewith the gate insulating film interposed therebetween; a source and adrain regions in contact with the channel formation region; a protectivefilm in contact with the channel formation region; and a darkenedorganic resin in contact with a part of the protective film, and formedover at least the channel formation region.
 2. A semiconductor devicecomprising: a pixel matrix circuit over an insulating surface, having aplurality of pixels, each of the plurality of pixels comprising at leasta thin film transistor, the thin film transistor comprising: a gate lineformed on the insulating surface; a gate insulating film in contact withthe gate line; a semiconductor film over the gate line with theinsulating film interposed therebetween, comprising a channel formationregion a source and a drain regions in contact with the channelformation region; a protective film in contact with the channelformation region; and a darkened organic resin in contact with a part ofthe protective film, and formed over the channel formation region.
 3. Asemiconductor device comprising: a pixel matrix circuit over aninsulating surface, having a plurality of pixels, each of the pluralityof pixels comprising at least a thin film transistor, the thin filmtransistor comprising: a gate line formed on the insulating surface; agate insulating film in contact with the gate line; a channel formationregion formed over the gate line with the gate insulating filminterposed therebetween; a source and a drain regions in contact withthe channel formation region; a protective film in contact with thechannel formation region; a darkened organic resin in contact with apart of the protective film, and formed over at least the channelformation region; and a layer insulating film over the darkened organicresin, wherein at least an edge of the darkened organic resin alignswith at least an edge of the channel formation region.
 4. Asemiconductor device comprising: a peripheral driving circuit over aninsulating surface, having a plurality of thin film transistors, each ofthe plurality of thin film transistor comprising: a gate line formed onthe insulating surface; a gate insulating film comprising a firstinsulating film comprising an organic material and a second insulatingfilm comprising silicon nitride over the first insulating film, incontact with the gate line; a channel formation region formed over thegate line with the gate insulating film interposed therebetween; asource and a drain regions in contact with the channel formation region;a protective film in contact with the channel formation region; and adarkened organic resin in contact with a part of the protective film,and formed over at least the channel formation region.
 5. Asemiconductor device comprising: a peripheral driving circuit over aninsulating surface, having a plurality of thin film transistors, each ofthe plurality of thin film transistor comprising: a gate line formed onthe insulating surface; a gate insulating film in contact with the gateline; a semiconductor film over the gate line with the insulating filminterposed therebetween, comprising a channel formation region, a sourceand a drain regions in contact with the channel formation region; aprotective film in contact with the channel formation region; and adarkened organic resin in contact with a part of the protective film,and formed over the channel formation region.
 6. A semiconductor devicecomprising: a peripheral driving circuit over an insulating surface,having a plurality of thin film transistors, each of the plurality ofthin film transistor comprising: a gate line formed on the insulatingsurface; a gate insulating film in contact with the gate line; a channelformation region formed over the gate line with the gate insulating filminterposed therebetween; a source and a drain regions in contact withthe channel formation region; a protective film in contact with thechannel formation region; a darkened organic resin in contact with apart of the protective film, and formed over at least the channelformation region; and a layer insulating film over the darkened organicresin, wherein at least an edge of the darkened organic resin alignswith at least an edge of the channel formation region.
 7. Asemiconductor device according to claim 1, wherein the semiconductordevice is in an electronic equipment selected from the group of a videocamera, a digital camera, a rear type or a front type projector, ahead-mount display, a goggle type display, a car navigation system, apersonal computer, a mobile computer, a portable telephone and anelectronic book.
 8. A semiconductor device according to claim 2, whereinthe semiconductor device is in an electronic equipment selected from thegroup of a video camera, a digital camera, a rear type or a front typeprojector, a head-mount display, a goggle type display, a car navigationsystem, a personal computer, a mobile computer, a portable telephone andan electronic book.
 9. A semiconductor device according to claim 3,wherein the semiconductor device is in an electronic equipment selectedfrom the group of a video camera, a digital camera, a rear type or afront type projector, a head-mount display, a goggle type display, a carnavigation system, a personal computer, a mobile computer, a portabletelephone and an electronic book.
 10. A semiconductor device accordingto claim 4, wherein the semiconductor device is in an electronicequipment selected from the group of a video camera, a digital camera, arear type or a front type projector, a head-mount display, a goggle typedisplay, a car navigation system, a personal computer, a mobilecomputer, a portable telephone and an electronic book.
 11. Asemiconductor device according to claim 5, wherein the semiconductordevice is in an electronic equipment selected from the group of a videocamera, a digital camera, a rear type or a front type projector, ahead-mount display, a goggle type display, a car navigation system, apersonal computer, a mobile computer, a portable telephone and anelectronic book.
 12. A semiconductor device according to claim 6,wherein the semiconductor device is in an electronic equipment selectedfrom the group of a video camera, a digital camera, a rear type or afront type projector, a head-mount display, a goggle type display, a carnavigation system, a personal computer, a mobile computer, a portabletelephone and an electronic book.